In comparison with a Long Term Evolution (LTE), peak rates of a Long Term Evolution Advanced (LTE-A) have increased greatly, which can reach 1 Gbps of downlink and 500 Mbps of uplink. However, a single carrier can not meet this demand, so Carrier Aggregation (CA) technique is introduced into the LTE-A system. The CA technique enable multiple carriers of the same eNB, which have overlapped coverage regions in a physical space, to be aggregated for serving a UE so as to provide the serve rates which the UE needs. The respective carriers involved in the CA are referred to as Component Carrier (CC) of the UE. Furthermore, in the LTE-A system, each cell of the eNB is defined to have only one carrier. Thus, the Carrier Aggregation enables one UE transmits data to the network with resources of plural cells belonging to one eNB.
In order to ensure normal operation of LTE UE in each LTE-A system, the maximum bandwidth of each carrier is required not to exceed 20 MHz in the LTE-A system. FIG. 1 is a schematic diagram showing the CA technique in the LTE-A of the prior art. As shown in FIG. 1, the eNB transmits data with the UE on four CC simultaneously so as to enhance throughput of the UE in the system.
For LTE-A and LTE UEs, there are four LTE-A cells of the eNB having the same coverage. However, for the LTE-A UE, the network can schedule resources of one or more cells for serving the UE according to the requirements of the serve rate of the UE, and for the LTE UE, the network can only schedule resources of one cell for serving the UE.
Currently, each activate UE (RRC-CONNECTED UE) in the LTE system has just one serving cell, thus the UE only needs to monitor one downlink carrier. The monitoring mechanism for the downlink carrier in the LTE system of the prior art is shown in FIG. 2. FIG. 2 is a structural diagram showing downlink subframes, each of which consists of OFDM symbols. The first 1-3 OFDM (Orthogonal Frequency Division Multiplexing) symbols of the downlink subframe are control symbols for bearing downlink control signalling. A channel bearing the downlink control signalling is referred to as PDCCH (Physical Downlink Control Channel). The rest of the OFDM symbols bear downlink data, and a physical layer channel bearing the downlink data is referred to as PDSCH (Physical Downlink Shared Channel). The control signalling may comprise: scheduling information of the present downlink subframe and a corresponding uplink subframe and the related HARQ (Hybrid Automatic Repeat Request) information etc. The UE determines whether the resources are allocated to the corresponding subframe with the received control signalling of the downlink subframe. If the resources are allocated, the UE obtains the time frequency position of the resources according to the indication of the scheduling signalling and performs data communication.
The prior art has the following disadvantages: as the CA technique is introduced into the LTE-A system, which enable the UE to configure the plurality of CC, one LTE-A UE may use a plurality of CC for data transmission simultaneously. When the LTE-A UE has to receive and send relative large amount of data, it is required to transmit data on the plurality of CC. Meanwhile, the UE monitors PDCCH and PDSCH on the plurality of CC. However, it is unnecessary to monitor the plurality of CC if there is not too much amount of data. Thus, the unused CC is stopped to receive and decode data so as to save power for the UE. When the UE has to receive and send relative large amount of data, the UE is enabled to monitor the corresponding CC.
For the LTE-A system, UE is required to monitor the carrier aggregation scheduled by the network. Therefore, the network should notify the UE that it decides to change the carriers aggregated for the LTE-A UE, so that the UE can activate or deactivate the monitoring of the corresponding CC in time. Accordingly, flexible configuration is achieved. The current LTE-A system still has no corresponding notifying mechanism.